High T(c) Oxide Superconducting Thin Films.

We have shown that pulsed laser deposition from a single target is simple, easy, and inexpensive compared to most of the other techniques employed for preparation of high T_{c} superconducting thin films. The pulsed laser deposition process can enable preparation of thin films of complex composition with good control over the film stoichiometry. The film compositions are similar to that of the target pellet, and independent of the substrate temperature and the oxygen partial pressure in the deposition system. The as-deposited Y-Ba-Cu oxide thin films on SrTiO_3 show zero resistance temperatures and critical current densities at 77 K of over 90 K and 4-5 times 10^ 6 A/cm^2 respectively, which are among the best results in the world. Both mass spectroscopic and x-ray absorption studies rule out the ejection of stoichiometric clusters of the material from the pellet during the laser deposition process. Instead, binary and ternary suboxides are emitted from the target pellet. It was found that a minimum energy density is needed to have stoichiometric deposition, and only the central region of the deposited film has the right composition. These results can be explained on the basis of a primary evaporation and a secondary forward-directed ejection process. High oxygen partial pressure has been found to be an important parameter for the pulsed laser deposition of as-deposited superconducting thin films with high T _{c} and J_ {c}. The problems associated with fabrication of high quality thin films of the new high T_{c } superconductors are discussed.